Rare earth element-halide environments in oxyhalide glasses

ABSTRACT

The present invention relates to an oxyhalide glass matrix including 0-70 mol. % SiO 2 , 5-35 mol. % Al 2 O 3 , 1-50 mol. % B 2 O 3 , 5-35 mol. % R 2 O, 0-12 wt. % F, 0-12 wt. % Cl, and 0 to 0.2 mol. % rare earth element, wherein R is Li, Na, K, Rb, or Cs. The present invention further relates to a method of producing the glass matrix and to a method of modifying the spectral properties of an oxyhalide glass.

This application claims benefit of provisional application No.60/067,245, filed Dec. 2, 1997.

FIELD OF THE INVENTION

The present invention relates to oxyhalide glasses and a method ofmaking the oxyhalide glasses, as well as to a method of modifying thespectral properties of the oxyhalide glass.

BACKGROUND OF THE INVENTION

Recently, transparent materials capable of efficient frequencyupconversion, most being various rare-earth ion-doped fluoride glassesand crystals, have received great attention due to the possibilities ofutilizing these materials to achieve blue or green solid state lasers.While no significant difference in upconversion efficiency is observedbetween fluoride glasses and single crystals, single mode optical fiberdoped with a low level of rare-earth ions can be drawn from fluorideglasses, bringing about highly efficient blue or green upconversionfiber lasers. Unfortunately, heavy metal fluoride glasses suffer certainundesirable attributes which have restricted their applications. Mostnotably, heavy metal fluoride glasses exhibit poor resistance todevitrification. U.S. Pat. No. 4,674,835 to Mimura et al. discusses thecrystallization problems of heavy metal fluoride glasses, one example ofwhich is termed ZBLAN, and the light scattering problems resultingtherefrom.

The great susceptibility of heavy metal fluoride glasses todevitrification also generates problems in forming large preforms.Crystallization at the interface between the core and cladding duringthe production of the preform causes problems in the most commonly usedmethods for preparing an optical fiber. That is, heavy metal fluorideglasses are quite prone to inhomogeneous nucleation, the consequence ofwhich being crystallization at the core and cladding interfaces,particularly during the drawing of the optical fiber. The resultingfibers are subject to serious scattering losses due to crystals in thefibers.

Devitrification of the heavy metal fluoride glasses is aggravated whenions necessary to impart differences in indices of refraction to thecore and cladding are added to the glass composition. Additional doping,for example, with rare earth metal ions, also tends to reduce thestability of the glass. As a consequence of those problems, research hasfocused on finding additives to the base fluoride glass compositionwhich will reduce the tendency of the glass to devitrify and to increasethe chemical stability thereof. In addition, the preparation of fluorideglasses requires the glass forming components to be reheated at hightemperatures. In addition, fluoride glasses cannot be melted in air, butrequire water-free, inert gas environment.

Most oxide glasses (such as silica oxide) are much more chemically andmechanically stable and are easier to prepare and more easily fabricatedinto rods, optical fibers, or planar waveguides than fluoride glasses.Unfortunately, due to their larger phonon energy, silica glasses arevery inefficient for infrared upconversion. It has also been shown thataddition of oxides into fluoride glasses to improve their stability isnot preferred since even a small addition of oxides will significantlyquench the upconversion luminescence.

Early in 1975, Auzel et al., J. Electrochem. Soc., 122:101 (1975)reported an interesting class of infrared (“IR”) upconversion materialswhich were prepared from classical glass-forming oxides (SiO₂, GeO₂,P₂O₆, etc. with PbF₂ and rare-earth oxides), and showed an efficiencynearly twice as high as LaF₃:Yb:Er phosphor. Since these kinds ofmaterials were comprised of inhomogeneous glassy and crystalline phasesand the embedded crystals were very large in size (around 10:m), theywere not transparent.

Wang et al., “New Transparent Vitroceramics Codoped With Er³⁺ and Yb³⁺For Efficient Frequency Upconversion,” Appl. Phys. Lett., 63(24):3268-70(1993) describes transparent oxyfluoride vitroceramics (also calledglass ceramics) containing oxides of large phonon energy like SiO₂ andAlO_(1.5) but showing IR to visible upconversion which was moreefficient than fluoride glass. The composition of Wang consistedessentially, expressed in terms of mole percent, of

SiO₂ 30 CdF₂ 20 AlO_(1.5) 15 YbF₃ 10 PbF₂ 24 ErF₃ 1

The glass produced from that composition was heat treated at 470EC todevelop microcrystallites which the authors stated did not reduce thetransparency of the body.

The authors posited that the Yb³⁺ and Er³⁺ ions were preferentiallysegregated from the precursor glass and dissolved into the microcrystalsupon heat treatment. The size of the microcrystallites was estimated bythe authors to range from about 20 nm; that size being so small thatlight scattering loss was minimal. The authors reported the upeonversionefficiency of their products to be about 2 to 10 times as high as thatmeasured on the precursor glass and other fluoride-containing glasses.However, the crystals which are formed in the Wang glass have a cubiclattice structure, which limits the concentration of some of thetrivalent rare-earth elements which can be incorporated into the glassceramic. Another problem with these materials is that they requirecadmium in the formulation. Cadmium is a carcinogen and, thus, its useis restricted. Further, the glass-ceramic in Wang does not appear tohave a broad flat emission spectra required for some amplifierapplications.

The present invention is directed toward overcoming these above-noteddeficiencies.

SUMMARY OF THE INVENTION

The present invention relates to an oxyhalide glass matrix whichincludes 0-70 mol. % SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. % B₂O₃, 5-35mol. % R₂O, 0-12 wt. % F, 0-12 wt. % Cl, and 0 to 0.2 mol. % rare earthelement, where R is Li, Na, K, Rb, or Cs.

Another aspect of the present invention relates to a method of makingthe glass matrix. The method includes providing glass forming componentsand treating the glass forming components under conditions effective toproduce the glass matrix.

Yet another aspect of the present invention relates to a method ofmodifying the spectral properties of an oxyhalide glass. The methodincludes altering the halide content of the oxyhalide glass where thespectral properties of the oxyhalide glass are modified.

The glass matrix of the present invention is highly desirable inapplications where there is a requirement for the glass to be fabricatedin air using standard melting techniques and batch reagents. Inaddition, the glasses of the present invention are more environmentallystable than fluoride or chloride glasses, and therefore, are moresuitable in real-world applications. Further, the glass matrix of thepresent invention allows rare earth elements to be loaded into thematrix at high concentrations. Further, the glass matrix of the presentinvention has a broad flat gain spectrum, allowing it to be tailored forspecific amplifier applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing the emission spectra of Er³⁺ in an oxideglass, Er³⁺ in a pure fluoride glass, and Er³⁺ in a potassiumboroaluminofluorosilicate glass.

FIG. 2 is a graph showing the effect on the absorption spectrum of Nd³⁺through the addition of fluorine to an alkali boroaluminosilicate glass.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an oxyhalide glass matrix whichincludes 0-70 mol. % SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. % B₂O₃, 5-35mol. % R₂O, 0-12 wt. % F, 0-12 wt. % Cl, and 0 to 0.2 mol. % rare earthelement, where R is Li, Na, K, Rb, or Cs.

The local bonding environments of rare earth elements (“REEs”) inglasses determine the characteristics of their emission and absorptionspectra. A number of factors influence the width, shape, and absoluteenergy of emission and absorption bands, including the identity of theanion(s) and next-nearest-neighbor cations, the symmetry of anyparticular site, the total range of site compositions and symmetriesthroughout the bulk sample, and the extent to which emission at aparticular wavelength is coupled to phonon modes within the sample.Fluoride and chloride glasses are useful hosts for optically active REE,because the fluorine or chlorine atoms surrounding the REEssubstantially impact REE emission and absorption spectra. The extremeelectronegativity of fluorine or chlorine lifts the degeneracy of theelectronic states of the REE, producing emission and absorption bandswhich differ substantially from those produced in oxide hosts: they arebroader, and have different relative intensities and, sometimes,different positions. They are also often blue-shifted relative to theirpositions in oxide glasses. In general, the absolute position and widthof an emission or absorption band shifts to lower energy as theelectronegativity of the surrounding anions decreases: for example, thetotal bandwidth of the Er³⁺ 1530 nm emission band in fluoride glasses,such as ZBLAN, is greater than in nearly any oxide glass, and thehigh-energy edge of the emission band in a fluoride glass is at a higherenergy than in an oxide glass. In certain systems, such as hybridoxyfluoride glasses, it is possible to obtain much of the bandwidth andgain flatness of a fluoride glass by creating environments for the REEthat are a combination of oxide and fluoride-like sites.

For optical amplifier applications, the region over which a convolutionof the emission and absorption is the flattest is the optimal windowthrough which to pass signals. Because both the position of the overallemission bands and the structure within the band vary from fluoride tooxide to chloride hosts, the window with optimal gain flatness alsovaries. Ideally one would like to obtain the broadest emission possiblein a single glass. Given the trends discussed above, the best possibleglass would combine fluoride+oxide, fluoride+chloride, orfluoride+oxide+chloride environments to produce a single broad emissionband. Indeed, with chloride environments involved, then it might bepossible to use the same glass for both 1.3:m and 1.5:m amplifierapplications.

Relative to oxide glasses, fluoride or chloride glasses also canaccommodate very high concentrations of REEs without incurringnonradiative losses, due to energy transfers between the REE. On theother hand, fluoride and chloride glasses must be prepared undercontrolled atmospheres, have extremely high coefficients of thermalexpansion, and are environmentally unstable compared to many oxideglasses, which complicates their use in real-world applications.Ideally, one would like glasses that produce the fluoride-likeenvironments for REEs while retaining the physical and chemicalcharacteristics of oxide glasses.

Accordingly, the present invention is directed to a broad range ofaluminosilicate oxide glasses in which halides, such as fluorine andchlorine, and REEs can be added in high concentrations. These glassesproduce halide-like environments for the REE. When fluorine alone as thehalide is added, this results in the spectral properties typical of purefluoride glasses, including broad emission spectra, improved emissionlifetimes, and relative band intensities like fluorides rather thanoxides. Likewise, when chlorine alone is added, this results in anoxychloride glass having the spectral properties of pure chlorideglasses. When a mixture of fluorine and chlorine is used, glasses can betailored to have desirable spectral properties for individualapplications. In particular, glasses having a broad, flat emissionspectra can be produced. A flat emission spectra is defined as thosespectra with less than 10% gain ripple over bands (or windows) up to 35nm wide. Further, addition of fluorine, chlorine, or mixtures thereofresults in improved dispersal of the REE throughout the glass, whichfacilitates higher REE loadings without degradation of lifetime.Although not meaning to be bound by theory, it is believed that higherconcentrations of REEs are possible, because they are dispersed inseparate locations and, accordingly, cannot physically interact witheach other.

The present invention relates to a glass matrix. Specifically, theinvention relates to a broad class of aluminosilicate oxide glasses inwhich a halide and a rare earth element (“REE”) can be added. Preferablehalides include fluorine and chlorine. Preferable REEs include Y, La,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

Preferably, the glass matrix is a R₂O—Al₂O₃—B₂O₃—SiO₂—F—Cl composition,where R is Li, Na, K, Rb, or Cs, and where the glass matrix is dopedwith one or more REEs. More preferably, the glass matrix includes 0-70mol. % SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. % B₂O₃, 5-35 mol. % R₂O, 0-12wt. % F, 0-12 wt. % Cl, and 0 to 0.2 mol. % REE, with from 25-60 mol. %SiO₂, 10-25 mol. % Al₂O₃, 3-35 mol. % B₂O₃, 10-25 mol. % R₂O, 0-10 wt. %F, and 0-12 wt. % Cl being especially preferred. Generally, the halideis present in the form of alkali/alkaline earth or aluminum halide.Preferably, the fluorine is expressed as Al₂F₆ and the chlorine isexpressed as Al₂Cl₆, where the fluorine is expressed as up to 14 mol. %Al₂F₆ and the chlorine is expressed as up to 7 mol. % Al₂Cl₆.

The glass matrix of the present invention includes at least two distinctlocations. In the first location, the halides are present. In the secondlocation, the oxides are present. The REE may be present in either ofthe two locations. Alternatively, the halides are present in separatelocations and the oxides are present in a separate location and the REEsare present in any or all of these separate locations. As discussedabove, because the halides and oxides are present in separate locations,and the REEs are dispersed in these separate locations, they are notphysically able to interact with each other. Thus, higher loadings ofREEs are possible. Accordingly, smaller amplifiers are possible whenmade out of the glass matrix of the present invention, because lesswaveguide material for the same amount of gain is needed.

If no boron is included in the oxyhalide glass formulation, the spectraproperties of the oxyhalide glass resemble those of the best oxideglasses, but REEs can be loaded at much higher concentrations beforenonradiative losses cause lifetime reductions.

As increasing amounts of boron are added to a fluorine-bearing glass,the spectra begins to approach those of pure fluoride glasses, and whenthe fluorine/boron molar ratio is 1:1 or greater, spectra essentiallyidentical to those of pure fluoride glasses (such as ZBLAN) areobtained. In particular, oxyhalide glasses having from 5 to 12 wt. %fluorine have emission spectral properties from 1450 to 1650 nm whichare essentially identical to those of a pure fluoride glass. Further,oxyhalide glasses having from 5 to 12 wt. % fluorine have absorptionspectral properties from 1450 to 1650 nm which are essentially identicalto those of a pure fluoride glass.

Additionally, as chlorine in increasing concentrations is added to theoxyhalide glass composition, spectral properties essentially identicalto those of pure chloride glasses are obtained. In particular, oxyhalideglasses having from 4.5 to 8.5 wt. % chlorine have emission spectralproperties from 1450 to 1650 nm which are essentially identical to thoseof a pure chloride glass. Further, oxyhalide glasses having from up to12 wt. % chlorine have absorption spectral properties from 1450 to 1650nm which are essentially identical to those of a pure chloride glass.

Substitutions of germanium and lead for silicon, gallium for aluminum orboron, and antimony for boron can be used to improve fluorescenceintensities and emission lifetimes, and also to modify liquidstemperatures, viscosity curves, expansivity, and refractive index. Theidentity of the alkali/alkaline earth can be varied to vary therefractive index and to increase or decrease thermal expansivity.Glasses containing optically active REEs can be co-doped with non-activeREEs (for example, Er co-doped with La or Y) to increase emissionlifetimes, or co-doped with optically active REEs (such as Er co-dopedwith Yb) to improve quantum efficiency. By varying bulk composition,glasses can be formed with optical properties transitional between purefluoride and pure oxide glasses, and between pure fluoride and purechloride glasses, and between pure chloride and pure oxide glasses, thusaffording maximum flexibility in optical properties. In particular,glasses having a broad flat emission spectra are possible.

Thus, the glass matrix of the present invention has absorption andemission characteristics that are effectively hybrids of the bestcharacteristics obtained in chloride, oxide, or fluoride glasses alone.However, unlike fluoride and chloride glasses, which must be fabricatedin an inert atmosphere, these glasses can be fabricated in air usingstandard melting techniques and batch reagents. In addition, theenvironmental stability of the hybrid glasses considerably exceeds thatof pure fluoride or chloride glasses. Moreover, the addition of fluorineallows the glass matrix to obtain much of the bandwidth and gainflatness of a fluoride glass by creating environments for the REE thatare a combination of oxide and fluoride-like sites. Furthermore, theaddition of chlorine to hybrid glasses of the present inventionsubstantially increases emission lifetimes relative to an oxide oroxyfluoride glass.

The properties of the glass matrix make it desirable for a number ofapplications. The glass matrix, with a compatible covering or cladding,can be formed into optically active devices, such as optical amplifiersor lasers. Further, the glasses may be used alone in planaramplification applications. In addition, the glass matrix may be used incombination with chlorine-free oxyfluoride clad glasses fordouble-crucible fiberization or rod-and-tube redraw. Further, it ispossible to tailor the emission/absorption spectrum of the disclosedglass matrix to “fill in holes” in the gain spectrum of conventionalamplifier materials, such as silica, or ZBLAN, in a hybrid amplifier toprovide a still greater degree of gain flatness than can be obtainedfrom any of these materials alone.

Another aspect of the present invention relates to a method of makingthe glass matrix. The glass matrix may be produced according to standardtechniques for making glasses. Preferably, the method includes providingglass forming components and treating the glass forming components underconditions effective to produce the glass matrix

Preferably, the treating step is achieved by melting the glass formingcomponents to produce a glass melt, forming the glass melt into a glassshape, and cooling the glass shape. Preferably, the components aremelted at a temperature of from about 1300E to about 1500EC for fromabout 2 to about 4 hours to produce the glass melt. Next, the glass meltis formed into a glass shape. Suitable forming procedures includerolling, pressing, casting, or fiber drawing. The glass shape is thenpreferably a patty, rod, sheet, or fiber. Subsequently, the glass shapeis cooled. The cooled glass shape is then annealed at a temperature offrom about 350E to about 450EC for from about 0.5 hours to about 2hours. The glass shape is then cooled after annealing to about roomtemperature.

Yet another aspect of the present invention relates to a method ofmodifying the spectral properties of an oxyhalide glass. The methodincludes altering the halide content of the oxyhalide glass where thespectral properties of the oxyhalide glass are modified.

As discussed above, by increasing the content of, for example, chlorineand fluorine in the oxyhalide glass, the spectral properties of theoxyhalide glass can be modified to be essentially identical to those ofa pure halide glass. When fluorine alone as the halide is added, thisresults in the spectral properties typical of pure fluoride glasses,including broad emission spectra, improved emission lifetimes, andrelative band intensities like fluorides rather than oxides. Inparticular, emission and absorption spectral properties are essentiallyidentical to those of pure fluoride glasses. Likewise, when chlorinealone is added, this results in an oxyhalide glass having spectralproperties essentially identical to pure chloride glasses, in particularthe emission and absorption spectra. When mixtures of chlorine andfluorine are added, spectral properties of a hybrid glass are obtained,where the spectral properties of the glass can range from a purefluoride to a pure chloride to a hybrid. In particular, a glasscontaining amounts of fluorine and chlorine can be tailored to suitspecific applications. It is highly desirable to produce a glasscontaining fluorine and chlorine such that the glass has a broad flatemission spectrum.

EXAMPLES Example 1 Glass Preparation Procedures

Various glasses were prepared by mixing together amounts of batchmaterials as shown in Table I below.

TABLE I Compositions (in mole %) 1 2 3 4 5 6 7 8 SiO₂ 30 30 30 30 30 5542.1 42.1 Al₂O₃ 18 19 19.8 12.5 13.5 5.25 6 6 Al₂F₆ 3 2 1.25 8.5 7.56.75 5.7 5.7 B₂O₃ 28 28 28 28 28 15 15.4 15.4 K₂F₂ 9 12 12 — — — — —K₂Cl₂ 10.5 7.5 6.75 3 6 — — 2 K₂O 1.5 1.5 2.25 18 15 18 17.3 15.3 Er₂O₃.03 .03 .03 .03 .03 .012 .011 .011 GeO₂ — — — — — — 13.5 13.5

Subsequently, the batch materials were ball milled and charged intocovered platinum crucibles. The crucibles were entered into anelectrically heated furnace held at from about 1300E to about 1500EC andmelted for from about 2 to about 4 hours. Next, the melts were pouredonto steel plates in order to form the melts into a glass shape. Themelts then were cooled. The cooled melts were placed into annealingovens and held at from about 350E to 450EC for one hour. Afterannealing, the furnaces were allowed to cool at furnace rate to roomtemperature.

Spectroscopic Analysis

The glass samples for spectroscopic analysis were polished piecesapproximately 20×20×5-10 mm. Absorption measurements were made using aNicolet FT-IR spectrophotometer (Madison, Wis.) with a 4 cm⁻¹ resolutionand collecting 256 FID's per sample. Fluorescence emission spectra of Erwas generated by pumping the 520 nm absorption with a Xenon lamp. The1.5 micron emission was measured using a liquid nitrogen cooled Sidetector in conjunction with a SPEX Fluorolog spectrophotometer (Edison,N.J.). Data was collected over the range 1400-1700 nm in 0.5 nm steps,counting for 1.5 seconds/step. For comparative purposes, a linearbackground was subtracted from each spectrum, with each spectrum thenbeing normalized to a value of 1.0 for the maximum peak intensity. Datafor the samples is provided in the examples below.

Example 2 Comparison of Emission Spectra of Er³⁺ in SiO₂, ZBLAN, andSample 9

The emission spectra of Er³⁺ in a silica oxide glass, ZBLAN (a purefluoride glass), and a glass in accordance with the present inventionwere determined for comparison. The spectra are shown in FIG. 1.

The present glass is a potassium boroaluminofluorosilicate glass havingthe composition shown below in Table II as Sample 9.

TABLE II Sample 9 mole % SiO₂ 55.60 Al₂O₃ 7.88 Al₂F₆ 3.82 K₂O 6.73 K₂F₂10.60 B₂O₃ 15.20 Er₂O₃ 0.012

The emission spectrum of Er³⁺ in the silica oxide glass was very similarto the spectrum obtained in typical fluorine-free aluminosilicateglasses. The emission spectrum of Er³⁺ in the Sample 9 glass, however,was identical to the spectrum of Er³⁺ in ZBLAN, indicating that Er³⁺ issurrounded by fluorine in the Sample 9 glass, much as in ZBLAN. Theflatness of the emission spectrum from 1530 to 1560 nm leads to acomparatively flat gain spectrum for ZBLAN. FIG. 1 shows that the samegain flatness can be obtained from the Sample 9 glass, but, unlikeZBLAN, it can be prepared in a conventional furnace.

Example 3 Comparison of Absorption Spectra of Nd³⁺ on Various Fluorideand Oxide Hosts

The optical absorption spectra of Nd³⁺ in various fluoride and oxidehosts were compared. Fluoroberylate and fluorozirconate hosts contain nooxygen, and this causes the relatively intense absorption band at 800 nmto blue shift to lower wavelength, and for it to be more intense orsubequal in intensity to the band at 580 nm. In phosphate, borate, andsilicate hosts containing no fluorine, the band near 800 nm wasred-shifted to higher wavelengths relative to the fluoride hosts, andwas less intense than the peak absorbance near 580 nm.

Example 4 Addition of Fluorine to an Alkali Boroaluminosilicate Glass

The effect of adding increased amounts of fluorine to alkaliboroaluminosilicate glasses similar to Sample 9 glass (shown in Example2) on the absorption spectrum of Nd³⁺ was investigated and is shown inFIG. 2. The results show that as fluorine concentration increased, thepeak absorbance near 800 nm increased in intensity relative to the 580nm peak and shifted to lower wavelengths, such that at 6.63 wt. % addedfluorine, the absorption spectrum represents that of Nd³⁺ influoroberylate hosts. Erbium is considered a heavy REE, whereasneodymium is considered a light REE. Therefore, the results indicatethat the fluoride-like environments are produced in the glass matrix ofthe present invention for both heavy and light rare earth elements.

Example 5 Comparison of Er³⁺ Emission and Absorption Spectra of AlkaliBoroaluminosilicate Glasses with Different Concentrations of Fluorine

The Er³⁺ emission spectra of alkali boroaluminosilicate glasses withdifferent concentrations of fluorine were compared with silica. As thelevel of fluorine increased, the relative intensity at 1530 nm decreasedat the expense of emission in the region from 1540-1560 nm, until at 9.6wt. % batched fluorine the emission spectrum was basically a smooth linefrom 1530 to 1560 nm. This creates many possibilities for producing flatgain amplifiers or hybrid amplifiers involving combinations of two ormore glasses.

As fluorine concentration increased, so too did the absorption featurenear 1.5 μm. In the glass with 9.6 wt. % batched fluorine, theabsorption spectrum was essentially identical to that of Er³⁺ in ZBLAN,a fluorozirconate glass having potential for fiber amplifierapplications. The extent to which the emission and absorption spectra ofEr³⁺ can be manipulated in these oxyfluoride glasses greatly exceeds thepossibilities in oxide or fluoride glasses alone. It opens upsignificant opportunities for 1.5 μm amplifiers and hybrid amplifiers.

Table III below shows the Er³⁺ emission lifetimes in alkaline earthaluminosilicate and alkali aluminosilicate glasses as a function offluorine concentration.

TABLE III wt. % F lifetime (ms) 0.0 6.9 3.5 7.0 6.0 7.0 7.0 8.1 10.0 8.713.4 8.9

The addition of increased amounts of fluorine to aluminosilicate glassessubstantially increased lifetimes (Table III), had a modest effect onthe shape of the emission spectrum, and greatly increased the amount ofREE that could be added before nonradiative losses reduced lifetimes.This effect was also observed in alkali boroaluminofluorosilicateglasses, although with much larger changes to the shape of the emissionspectrum.

Representative composition limits for oxyfluoride glasses of the presentinvention are shown in Table IV.

TABLE IV Oxide Mole % SiO₂ 0-70 Al₂O₃ 0-30 B₂O₃ 0-30 R₂O 0-35 Er₂O₃ ≦0.5(Y,La,Gd)₂O₃ ≦10x Er₂O₃ F 2-20 (wt. %)

Example 6 Comparison of the 1530 Er³⁺ Absorption Spectrum of anOxyfluoride Glass with a Glass of the Same Overall Composition butContaining 0.9 wt. % Cl

The 1530 Er³⁺ absorption spectrum of an oxyfluoride glass (sample 7 asprepared in Example 1 containing 8.5 wt. % F) was compared with a glassof the same oberal composition but additionally containing 0.9 wt. % Cl(sample 8 as prepared in Example 1). Addition of Cl to the glass shiftedthe absorption spectrum to a longer wavelength (˜7 nm), showing that Clis intimately associated with the REE in the glass, even at thisrelatively low concentration. There was a corresponding shift in theposition of the primary emission line (from 1530 nm to approximately1537 nm). Much higher chlorine retentions and overall chloride levelswere obtained in glasses with M₂O/Al₂O₃ ratios of 1.0 or less, withcomparable effects on the absorption and emission spectra.

Example 7 Comparison of the 1530 nm Er³⁺ Absorption Spectrum in ZBLANNear 1520 nm with Spectra Obtained from Glasses in this SystemContaining Varying Amounts of Fluorine and Chlorine

The 1530 nm Er³⁺ absorption spectrum in ZBLAN near 1520 nm was comparedwith spectra obtained from the specified glasses produced in Example 1and having the halide composition shown in Table V below.

TABLE V glass wt. % Cl wt. % F 4 2.4 10.6 5 4.7 9.2 3 5.4 6.7 2 5.9 7.51 8.0 7.3

The absorption spectrum of sample 4 was qualitatively similar to that ofZBLAN, though its emission spectrum was very much broader. Replacingincreasing amounts of fluorine with chlorine caused a large red-shift ofthe main absorption line to nearly 1540 nm while preserving the positionof the blue-edge of the band near 1495 nm. At the highest chlorineconcentration in this series (sample 1), the spectrum resembled that ofa pure chloride glass. Because the main absorption band shifted tosteadily longer wave length without bifurcating, the environmentsrepresented by the intermediate compositions are not simply sums of theendmembers (samples 4 and 1), but hybrid sites or sums of many hybridsites with variable anion contents.

Example 8 Comparison of the Emission Spectra of ZBLAN and Samples 6 and4

The emission spectra of ZBLAN and sample 6 (as prepared in Example 1)were compared with that of sample 4 (as prepared in Example 1). Theemission spectrum of sample 4 was far broader than those of otherglasses, extending from 1525 nm to more than 1570 nm. The lifetime ofthe erbium emission was also increased as chlorine was added to theglass. These results indicate that the shape of the emission spectrumcan be adjusted considerably by varying the relative proportions offluorine and chlorine and by varying the proportions of both of thesewith respect to oxygen. To the extent that chlorine alone is insertedinto the rare earth environment, these glasses are also potentiallyattractive as hosts for Dy, Nd, and Pr in 1.3:m amplifier applications.

Although the invention has been described in detail for the purpose ofillustration, it is understood that such detail is solely for thatpurpose, and variations can be made therein by those skilled in the artwithout departing from the spirit and scope of the invention which isdefined by the following claims.

What is claimed:
 1. An oxyhalide host glass for a rare earth element,the glass having a composition consisting essentially of 0-70 mol. %SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. % B₂O₃, 5-35 mol. % R₂O where R isLi, Na, K, Rb or Cs, and an amount up to 0.2 mol. % rare earth element,and in wt. %, an amount up to 12% of F, Cl or mixtures.
 2. An oxyhalideglass matrix comprising 0-70 mol. % SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. %B₂O₃, 5-35 mol. % R₂O, an amount up to 12 wt.% F, 0-12 wt. % Cl, and 0and 0.2 mol. % rare earth element, wherein R is Li, Na, K, Rb or Cswherein the fluorine is present in Al₂F₆.
 3. An oxyhalide glass matrixcomprising 0-70 mol. % SiO₂, 5-35 mol. % Al₂O₃, 1-50 mol. % B₂O₃, 5-35mol. % R₂O, 0-12 wt. % F, an amount up to 12 wt. % Cl, and 0 and 0.2mol. % rare earth element, wherein R is Li, Na, K, Rb or Cs wherein thechlorine is present in Al₂Cl₆.
 4. The glass matrix according to claim 1,wherein the rare earth element is selected from the group consisting ofY, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. 5.The glass matrix according to claim 4, wherein the glass matrix includesat least two rare earth elements.
 6. The glass matrix according to claim1, wherein Cl and F are present at a first location within the glassmatrix and the oxides are present at a second location within the glassmatrix, wherein the first location is distinct from the second location.7. The glass matrix according to claim 6, wherein the rare earth elementis partitioned into the first location.
 8. The glass matrix according toclaim 6, wherein the rare earth element is partitioned into the firstand second locations.
 9. The glass matrix according to claim 6, whereinthe rare earth element is partitioned into the second location.